pytorch

eb4238fc - Allow caffe2-specific graph transformations for OperatorExportTypes.ONNX_ATEN_FALLBACK when BUILD_CAFFE2 is ON (#67460) (#68490)

Allow caffe2-specific graph transformations for OperatorExportTypes.ONNX_ATEN_FALLBACK when BUILD_CAFFE2 is ON (#67460) (#68490) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/68490 The use of ATEN as a fallback operator during ONNX conversion is important for increasing operator coverage or even provide more efficient implementations over some ONNX ops. Currently this feature is available through `OperatorExportTypes.ONNX_ATEN_FALLBACK`, but it also performs changes to the graph that are runnable by Caffe2, only. This PR introduces restricts caffe2-specific graph transformations for `ONNX_ATEN_FALLBACK` operator export type for when pytorch is built with caffe2 support (aka BUILD_CAFFE2=1 during build) The first version of this PR introduced a new operator export type `ONNX_ATEN__STRICT_FALLBACK`, which essentially is the same as `ONNX_ATEN_FALLBACK` but without caffe2 transformations. It was preferred to not introduce a new operator export type, but to refine the existing aten fallback one ## BC-breaking note ### The global constant `torch.onnx.PYTORCH_ONNX_CAFFE2_BUNDLE` is removed in favor of a less visible `torch.onnx._CAFFE2_ATEN_FALLBACK`. `PYTORCH_ONNX_CAFFE2_BUNDLE` is really a dead code flag always set to False. One alternative would be fixing it, but #66658 disables Caffe2 build by default. Making a Caffe2 feature a private one seems to make more sense for future deprecation. ### The method `torch.onnx.export` now defaults to ONNX when `operator_export_type` is not specified. Previously `torch.onnx.export's operator_export_type` intended to default to `ONNX_ATEN_FALLBACK` when `PYTORCH_ONNX_CAFFE2_BUNDLE` was set, but it would never happen as `PYTORCH_ONNX_CAFFE2_BUNDLE` is always undefined Co-authored-by: Nikita Shulga <nshulga@fb.com> Test Plan: Imported from OSS Reviewed By: jansel Differential Revision: D32483781 Pulled By: malfet fbshipit-source-id: e9b447db9466b369e77d747188685495aec3f124 (cherry picked from commit 5fb1eb1b1973e47a8215978e96dd1284570f13e6)